What is the average risk of developing breast cancer?

8 Jan

What is the average risk of developing breast cancer?

Breast cancer risk rises with age; in NZ over 70% of new cases are among women 50 years and over.

In NZ, the current (as of late 2009)  lifetime risk (for women) for developing breast cancer was 1 in 9.

Http://www.nzbcf.org.nz/component/content/article/9-news/238-breast-cancer-in-new-zealand

In the USA, it is 1 in 8.

http://www.cancer.gov/cancertopics/factsheet/Detection/probability-breast-cancer

In NZ, according to the The New Zealand Breast Cancer Foundation “Breast Health Education Kit 2010:  Risk and Risk Reduction Factors for Breast Cancer February 2010” (downloadable from the NZ Breast Cancer Foundation website), for New Zealand women current average risks of developing breast cancer by decade of age are as follows:

“Age               Risk                      Risk Percent
30s                 1 in 204                (0.5%)
40s                 1 in 67                  (1.5%)
50s                 1 in 35                  (2.8%)
60s                 1 in 33                  (3.0%)
70s                 1 in 38                  (2.6%)”

It appears that the breast cancer risk for NZ women in their 30s, 40s and 50s is higher than for American women in the same age groups. (It is also possible that different techniques are used to determine cancer risk.)

The US National Cancer Institute’s (NCI) Surveillance, Epidemiology, and End Results (SEER) Program has published its SEER Cancer Statistics Review 1975–2007 includes estimates of  the probability of American women being diagnosed over several different decades of their adult lives.

The information below is excerpted from the following website:

http://www.cancer.gov/cancertopics/factsheet/Detection/probability-breast-cancer

“What is the average American woman’s risk of being diagnosed with breast cancer at different ages? The estimated probability of being diagnosed with breast cancer for specific age groups and for specific time periods is generally more informative than lifetime probabilities. Estimates by decade of life are less influenced by changes in life expectancy and incidence rates. The SEER report estimates the risk of developing breast cancer in 10-year age intervals (1). These calculations factor in the proportion of women who live to each age. In other words, they take into account that not all women live to older ages, when breast cancer risk becomes the greatest.

A woman’s chance of being diagnosed with breast cancer is:

“from age 30 through age 39 . . . . . . 0.43 percent (often expressed as “1 in 233”)
“from age 40 through age 49 . . . . . . 1.45 percent (often expressed as “1 in 69”)
“from age 50 through age 59 . . . . . . 2.38 percent (often expressed as “1 in 42”)
“from age 60 through age 69 . . . . . . 3.45 percent (often expressed as “1 in 29”)

“These probabilities are averages for the whole population. An individual woman’s breast cancer risk may be higher or lower, depending on a number of factors, including her family history, reproductive history, race/ethnicity, and other factors that are not yet fully understood.

“To calculate an individual’s estimated risk, see the Breast Cancer Risk Assessment Tool at http://www.cancer.gov/bcrisktool/ on the Internet. For more information on the subject of lifetime risk of breast cancer, see http://surveillance.cancer.gov/statistics/types/lifetime_risk.html on the Internet.

“Selected Reference

Altekruse SF, Kosary CL, Krapcho M, et al. SEER Cancer Statistics Review, 1975–2007. Bethesda, MD: National Cancer Institute, 2010.”

Commentary

The fact that there are no figures for women under 30 for either the NZ or US data does not mean that women in their 20s or teens never get breast cancer.  However it is a rare disease in very young women.   Women older than 80 can also develop breast cancer as well. However, data for these older age groups was not included on the websites from which I excerpted the statistics.

Both the NZ and US figures do give a good idea of how breast cancer incidence rises with age.  However, in each case the figures refer only to “average” risk.  Personal risk can be influenced by many factors, not all of which are included as variables in the Breast Cancer Risk Assessment Tool mentioned above, meaning that the accuracy of the Breast Cancer Risk Assessment Tool is open to question.  (For more information about factors that increase breast cancer risk please see the post: “Breast Cancer Risk Factors and Prevention Strategies”.

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